Method of and apparatus for disintegrating and dispersing a molten smelt stream



Jan. l0, 1961' B. METHOD 0F' AND APPARA AND DISPERSING A N -THORSON T USFOR DISINTEGRATING MOLTEN SMELT STREAMV Original Filed Jan. 8, 1952ATTORNEY United States Patent() IVIETHOD OF AND APPARATUS FOR DISINTE-GRATING AND DISPERSING A MOLTEN SMELT STREAM Benjamin N. Thorson,Seattle, Wash., assignor to The Babcock & Wilcox Company, New York,N.Y., a corporation of New Jersey Continuation of application Ser. No.265,433, Jan. 8, 1952. This application June 21, 1956, Ser. No. 592,987

s claims. (cl. :z3-4s) The present invention relates to the recovery ofchemi cals by the incineration of a pulp residual liquor, and moreparticularly to a method of and apparatus for disintegrating anddispersing a stream of molten smelt prior to its delivery to a pool ofliquid in a dissolving tank so as to avoid or at least minimize violentchemical reactions in the dissolving tank. This application is acontinuation of my copending application Serial No. 265,433, filedJanuary 8, 1952, now abandoned.

In the sulphate and soda processes for the digestion of cellulosicfibrous materials, the residual liquor from the digestors is incineratedwith the recovery of the sodium salts in the form of a molten smeltwithdrawn from the incinerating zone and discharged into a dissolvingtank, which is partly filled with a pool of weak liquor obtained fromthe causticizing portion of the process. In the sulphate process, thesmelt is mainly composed of sodium carbonate and sodium sulphide, thelatter resulting from the reduction of sodium sulphate in the char bed.In the soda process, the smelt is mainly sodium carbonate. The aqueousliquor in the dissolving tank is highly reactive chemically to thesemolten sodium compounds, particularly when they are allowed toaccumulate in masses. Discharging the molten smelt as a continuousstream into the liquid within the dissolving tank has been accompaniedby noise in the nature of a continuous roar at a high sound level, andoccasionally by violent and destructive explosions. Many attempts havebeen made to eliminate or reduce this noise, but such attempts have notheretofore been successful.

According to my present invention, dissolving tank noise has beenlargely eliminated by the use of a high velocity gaseous uid jet,preferably steam under a substantial pressure, which is directeddownwardly tohintercept the stream of molten smelt entering thedissolving tank so as to shatter the stream and disperse the smeltparticles before the molten smelt encounters the pool of weak liquor inthe tank. The downward direction of the smelt disintegrating jet drivesthe smelt particles towards the pool and during this travel the smeltparticles are preferably quenched by a spray of weak liquor recirculatedfrom the pool. Within certain definite limits as to gaseous fluid flow,and jet nozzle location, my invention has been found to practicallyeliminate the dissolving tank noise and explosions heretofore common inthe industry.

The various features of novelty which characterize my invention arepointed out with particularity in the claims annexed to and forming apart of this specification. For a better understanding of the invention,its operating advantages and specific objects attained by its use,reference should be had to the accompanying drawings and descriptivematter in which I have illustrated and described an embodiment of myinvention.

Of the drawings:

Fig. 1 is a sectional elevation taken on the line 1-1 -Qf Fig. 2 ofapparatus incorporating the invention;

"ice

Fig. 2 is a plan of the apparatus shown in Fig. 1; and

Figs. 3 and 4`are side and end views, respectively, of the nozzle shownin Fig. 1.

In the drawings, the invention is illustrated as applied todisintegrating and dispersing the stream of molten smelt discharged froma chemical recovery furnace of the general type illustrated in U.S.Patent No. 2,161,110, before the molten smelt enters a pool ofdissolving liquor. In the process of chemical recovery disclosed in thepatent the molten smelt is obtained by the incineration of residualliquor resulting from the soda or sulphate processes of paper pulpmanufacture, so that the smelt contains mainly sodium carbonate and/orsodium sulphide.

As shown, a pair of discharge spouts 10 from th hearth 11 of therecovery furnace 12 extend outwardly with a downward inclination fromcorresponding ports in the front wall 13 of the furnace. From the end 14of each discharge spout 10, the molten chemical smelt tends to fallcontinuously in a substantially solid stream through a downwardtrajectory into a pool of weak liquor maintained in a dissolving tank15. In the processes described, the molten smelt leaving the furnace 12will be at a temperature between 1500 and 1700 F. The smelt is dissolvedin the weak liquor within the tank 15, with the concentrated liquorcontinuously withdrawn, and make-up weak liquor continuously added tomaintain the level of the liquor pool in the tank substantially constantas, for example, at 16. The temperature of the liquor pool within thetank 15 will ordinarily be of the order of 15G-200 F.

Customarily the tank is provided with an agitator 17 mounted on avertical shaft 1S and driven by a motor 20. ln addition, liquor iswithdrawn from the lower portion of the tank 15 by a pump 21 through thevalved connection 22 and returned through pipes 23 and nozzles 24 to theupper portion of the tank above the normal pool nozzle is used in smallcapacity recovery units While a pair of spouts are used in high capacityrecovery units. Whatever the capacity of the recovery unit, each spout10 is provided with an enclosing hood 25 which extends upwardly from anopening in the tank cover 26 toward the furnace wall 13. The cover 26 isreinforced by structural steel members 27 which also support the motor20 and drive mechanism for the agitator 17. A vent port 28 is providedin the cover of the tank and is usually connected with a vent duct (notshown) to convey fumes and vapor developed in the tank to a dischargepoint located outside of the enclosure of the chemical recovery unit.

In the usual operation of a chemical recovery unit of the typedescribed, the stream of molten smelt discharging from the end of aspout 10 describes a downwardly curved trajectory in falling to thesubjacent liquor pool` The stream of liquor discharged from the nozzle24 strikes against the faling smelt stream and tends to de- -fleet andbreak up the smelt stream. However, the

effect of the recirculated liquor stream is insufficient to smelt streamis apparently due to the relativelyV low f velocity and directionthereof, and the prohibitive' pumping costs necessary to recirculate theliquor through the nozzles 24 at an adequate velocity to accomplish thesmelt stream shattering effect, as hereinafter described, for noiseelimination.

In accordance with the present invention, I have found that the usualnoise and explosions associated with dissolving tank operations in thechemical recovery process described can be substantially eliminated bythe use of a gaseous uid jet impacting the smelt stream at suillcientvelocity to disintegrate or shatter the smelt stream and to disperse orscatter the smelt particles over a re atively large horizontal area ofcontact with the liquor stream from nozzle 24 or with the upper surfaceof the pool within the tank 15. I prefer to use steam for this purposebecause in its expansion to atmospheric pressure the desired high jetvelocity is readily attainable. Steam is economically available inchemical recovery installations of the type described, since thequantity or steam required is less than one percent of the steamgenerated in the heat recovery portion of the residual liquorincinerating process.

Some reduction in noise can be attained by the use of a disintegratingand dispersing jet striking the smelt stream from almost any direction,providing large quantities of high velocity iluid is used. When a jet ofwater or weak liquor is horizontally directed against the smelt streamwith sufllciently high Velocity and in suilicient quantity to reduce thenoise by disintegration and dispersion of the smelt stream, the addedliquor dilutes the liquor pool in the tank to an excessive extent. Whenan air jet is used in this position, the vent discharge through theoutlet 28 is greatly increased. The power necessary to supply thenecessary high velocity jet of water, liquor or air is also excessive,under these conditions. However, for best results, with a reasonablequantity of gaseous fluid the direction of jet llow and the point ofcontact between the jet and the smelt stream must be selected withinclosely dened limits.

In Figs. 1 and 2, a nozzle 30 is positioned beyond the end 14 of eachspout 1t) with the longitudinal axis of the nozzle lying in a verticalpane common with the longitudinal axis of the spout 10 and spaced fromthe end of the spout so that an extension of the nozzle axis intersectsthe smelt stream where the trajectory is downward. I prefer that theminimum dimension between the axis of the nozzle 30 and the end 14 ofthe spout should be approximately 12 inches, and that the discharge endof the nozzle be substantially in horizontal alignment with the end 14of the spout. When the nozzle is used with the customary commercialsized chemica recovery units the axis of the nozzle 30 will besubstantially vertical, although under conditions of a relatively low orunusually high smelt flow rate the adjustable nozzle may be tilted a fewdegrees about the pivot 33 from the vertical to obtain best results.With the nozzle 30 located as described, the steam jet Issuing therefromwill strike the smelt stream about 6 or 7 inches from the nozzle tip.With proper steam ow, as hereinafter described, the jet will shatter thesmelt stream so that the smelt is dispersed into minute particles whichare quenched and further distributed upon contacting the liquor streamfrom the correspondin g nozzle 24 and dissolved upon entering the poolof dissolving liquor in the lower portion of the tank 15. Any smeltsplattered upon the wall of the tank is rcmoved by liquor washingobtained by low pressure jets supplied from the pipe 29.

'lhe theoretical reasons for the outstanding noise eliminating successof the described jet are obscure, but are probably due to severalfactors, such as the cooling effect upon the smelt in Contact with thesteam, the small size of the smelt particles entering the liquor pooland their distribution over a wide area of the liquor pool surface,

lrlidthe downward impetus given the smelt particles by e jet.

It has been observed that a minimum dimension of 3 feet, and preferably4 or 5 feet, should be provided b; tween the zone of jet contact withthe smelt stream and the stream of recirculated liquor discharged by thecorresponding nozzle 24. Under these conditions the rccirculated liquorfrom each nozzle 24 will intercept at least some of the smelt particlesand cause them to deposit over an increased area of the liquor pool.

The steam jet discharged through each nozzle 30 receives steam from anyconvenient source, such as from the steam generating equipment (notshown) associated with the furnace 12, through a valved pipe 31. In theembodiment shown, the steam is delivered to the nozzle 30 at a pressureof the order of 50 to 150 p.s.i.g. (pounds per square inch guage)depending upon the valve adjustment in the pipe 31. At this pressure,adequate steam llow is obtained by the use of a 3/e diameter pipe, andthe corresponding nozzle shown in Figs. 3 and 4, is fabricated byflattening a 1/2 pipe to an elongated tip 32, l by l, and having an areaof approximately .O6 square inch. Under these conditions, the jet steamllow will be of the order of 300 to 500 pounds per hour, and the steamvelocity will approach the acoustical veocity, i.e. of the order of 1200feet per' second. When higher pressure steam is available, the pipesizes and nozzle dimensions will be correspondingly reduced to retainthe equivalent jet velocity.

It will be noted that the dissolving tank noise customarily present inchemical recovery units of the type described, is effectively reduced oreliminated by the use of jets positioned as described so as todisintegrate and disperse the molten chemical stream before contactingthe pool of dissolving liquid. Steam is particularly eilective due toits high velocity, compared to other fluid mediums even though the massflows of all the mediums are substantially equal.

While in accordance with the provisions of the statutes I haveillustrated and described herein the best form of the invention nowknown to me, those skilled in the art will understand that changes maybe made in the form of the arparatus disclosed without departing fromthe spirit of the invention covered by the claims.

What is claimed is:

1. A process for the recovery of chemicals from pulp residual liquorcomprising the steps of incinerating a sodium base pulp residual liquorcontaining combustible organic and non-combustible inorganic chemicalsin an incinerating zone and reducing the inorganic chemicals to a moltenmetal smelt containing one or both compounds from the group of sodiumcarbonate and sodium sulphide, gravitationally discharging the moltensmelt as a substantially continuous stream from said incinerating zonein a downward trajectory towards a pool of aqueous dissolving liquorchemically reactive to said smelt, and disintegrating and dispersingsaid stream of smelt while above the level of said pool of dissolvingliquor by discharging a downwardly directed jet of gaseous fluidintersecting said smelt stream at a position of substantial verticaltangency while at a high jet velocity and driving said disintegrated anddispersed smelt into said pool of dissolving liquor.

2, A process for the recovery of chemicals from pulp residual liquorcomprising the steps of incinerating a sodium base pulp residual liquorcontaining combustible organic and non-combustible inorganic chemicalsin an incinerating zone and reducing the inorganic chemicals to a moltensmelt containing one or both compounds from the group of sodiumcarbonate and sodium sul phide, gravitationally discharging the moltensmelt as a substantially continuous stream from said incinerating zonein a downward trajectory towards a pool of aqueous dissolving liquorchemically reactive to said smelt, and disintegrating and dispersingsaid stream of smelt while above the level of said pool of dissolvingliquor by discharging a downwardly directed jet of steam intersectingsaid smelt stream at a position of substantial vertical tangency whileat a high jetv velocity approaching 1200 feet per second and drivingsaid disintegrated and dispersed smelt into said pool of dissolvingliquor.

3. A process for the recovery of chemicals from pulp residual liquorcomprising the steps of incinerating a sodium base pulp residual liquorcontaining combustible organic and non-combustible inorganic chemicalsin an incinerating zone and reducing the inorganic chemicals to a moltensmelt containing one or both compounds from the group of sodiumcarbonate and sodium sulphide, gravitationally discharging the moltensmelt as a substantially continuous stream from said incinerating zonein a downward trajectory towards a pool of aqueous dissolving liquorchemically reactive to said smelt, disintegrating and dispersing saidstream of smelt while above the level of said pool of dissolving liquorby discharging a downwardly directed jet of gaseous Huid intersectingsaid smelt stream at a position of substantial vertical tangency whileat a high jet velocity and driving said disintegrated and dispersedsmelt into said pool of dissolving liquor, and withdrawing aqueousliquor from said pool and spraying the withdrawn liquor in a generallyhorizontal direction into contact with the disintegrated and dispersedsmelt stream while above the level of said pool.

4. Chemical recovery apparatus comprising in combination a chemicalrecovery furnace having means for incinerating a sodium base pulpresidual liquor containing combustible organic and non-combustibleinorganic chemicals and reducing the inorganic chemicals to a moltensmelt containing one or both compounds from the group of sodiumcarbonate and sodium sulphide, and a smelt spout opening from saidfurnace for a gravitational discharge of a substantially continuousstream of molten smelt from said furnace, a smelt dissolving tankpositioned to receive the smelt stream discharging from said spout,means for maintaining in said dissolving tank a pool of aqueous liquorchemically reactive to said smelt, and means for disintegrating anddispersing said stream of smelt while above the level of said pool ofaqueous liquor including a gaseous fluid jet nozzle positioned above andspaced from the discharge end of said smelt spout to direct a highvelocity jet of gaseous fluid downwardly in substantially verticallytangential merging relationship with said smelt stream above the levelof said pool of aqueous liquor.

5. Chemical recovery apparatus comprising in combination a chemicalrecovery furnace having means for incinerating a sodium base pulpresidual liquor containing combustible organic and non-combustibleinorganic dhemicals and reducing the inorganic chemicals to a moltensmelt containing one or both compounds from the group of sodiumcarbonate and sodium sulphide, and a smelt spout opening from saidfurnace for a gravita- 'tional discharge of a substantially continuousstream of melten smelt from said furnace, a smelt dissolving tankpositioned to receive the smelt stream discharging from said spout,means for maintaining in said dissolving tank a pool of aqueous liquorchemically reactive to said smelt, and means for disintegrating anddispersing said stream of smelt while above the level of said pool ofaqueous liquor including a downwardly directed gaseous uid jet nozzlehaving its axis of discharge lying in a vertical plane common with theaxis of said smelt spout and positioned superjacent to the downwardtrajectory of said smelt stream to project a high velocity jet ofgaseous uid in vertically tangential relation and intersecting saidsmelt stream above the level of said pool of aqueous liquor.

6. Chemical recovery apparatus comprising in combination a chemicalrecovery furnace having means for incinerating a sodium base pulpresidual liquor containing combustible organic and non-combustibleinorganic chemicals and reducing the inorganic chemicals to a moltensmelt containing one or both compounds from the group of sodiumcarbonate and sodium sulphide, and a smelt spout opening from saidfurnace for a gravitational discharge of a substantially continuousstream of molten smelt from said furnace, a smelt dissolving tankpositioned to receive the smelt stream discharging from said spout,means for maintaining in said dissolving tank 'a pool of aqueous liquorchemically reactive to said smelt, and means for disintegrating anddispersing said stream of smelt while above the level of said pool ofaqueous liquor including a downwardly directed steam nozzle having itsaXis of discharge lying in a vertical plane common with the axis of saidsmelt spout and positioned superjacent to the downward trajectory ofsaid smelt stream to project a high velocity jet of steam substantiallyvertically tangentially intersecting said smelt stream above the levelof said pool of aqueous liquor.

7. Chemical recovery apparatus comprising in combination a chemicalrecovery furnace having means for incinerating a sodium base pulpresidual liquor containing combustible organic and non-combustibleinorganic chemicals and reducing the inorganic chemicals to a moltensmelt containing one or both compounds from the group of sodiumcarbonate and sodium sulphide, and a smelt spout opening from saidfurnace for a gravitational discharge of a substantially continuousstream of molten smelt from said furnace, a smelt dissolving tankpositioned to receive the smelt stream discharging from said spout,means for maintaining in said dissolving tank a pool of aqueous liquorchemically reactive to said smelt, and means for disintegrating anddispersing said stream of smelt while above the level of said pool ofaqueous liquor including means for horizontally projecting a spray ofcooling liquid above the level of said pool of aqueous liquor, adownwardly directed nozzle having its axis of discharge horizontallyspaced from the discharge end of said smelt spout and lying in avertical plane common with the axis of said smelt spout and positionedto project a high velocity jet of gaseous liuid substantially verticallytangentially intersecting said smelt stream at least three feet abovethe level of said spray of cooling liquid.

8. Chemical recovery apparatus comprising in combination a chemicalrecovery furnace having means for incinerating a sodium base pulpresidual liquor containing combustible organic and non-combustibleinorganic chemicals and reducing the inorganic chemicals to a moltensmelt containing one or both compounds from the group of sodiumcarbonate and sodium sulphide, and a Y smelt spout opening from saidfurnace for a gravitational discharge of a substantially continuousstream of molten smelt from said furnace, a smelt dissolving tankpositioned to receive the smelt stream discharging from said spout,means for maintaining in said dissolving tank a pool of aqueous liquorchemically reactive to said smelt, and means for disintegrating anddispersing said stream of smelt while above the level of said pool ofaqueous liquor including a downwardly directed nozzle positionedsuperjacent to the downward trajectory of said smelt stream and arrangedto project a high velocity jet of gaseous fluid in vertically tangentialintersecting relationship with said smelt stream above the level of saidpool of aqueous liquor, and means for withdrawing aqueous liquor fromsaid dissolving tank and spraying the withdrawn liquor into contact withthe gaseous uid jet disintegrated and dispersed smelt stream while abovethe level of said pool.

References Cited in the iile of this patent UNITED STATES PATENTS996,132 Perkins et al. .Tune 27, 1911 2,007,799* Gloersen July 9, 19352,163,148 Linder June 20, 1936 2,524,753 Betts Oct. 10, 1950 2,593,503Tomlinson et a1 Apr. 22, 1952

1. A PROCESS FOR THE RECOVERY OF CHEMICALS FROM PULP RESIDUAL LIQUORCOMPRISING THE STEPS OF INCINERATING A SODIUM BASE PULP RESIDUAL LIQUORCONTAINING COMBUSTIBLE ORGANIC AND NON-COMBUSTIBLE INORGANIC CHEMICALSIN AN INCINERATING ZONE AND REDUCING THE INORGANIC CHEMICALS TO A MOLTENMETAL SMELT CONTAINING ONE OR BOTH COMPOUNDS FROM THE GROUP OF SODIUMCARBONATE AND SODIUM SULPHIDE, GRAVITATIONALLY DISCHARGING THE MOLTENSMELT AS A SUBSTANTIALLY CONTINUOUS STREAM FROM SAID INCINERATING ZONEIN A DOWNWARD TRAJECTORY TOWARDS A POOL OF AQUEOUS DISSOLVING LIQUORCHEMICALLY REACTIVE TO SAID SMELT, AND DISINTEGRATING AND DISPERSINGSAID STREAM OF SMELT WHILE ABOVE THE LEVEL OF SAID POOL OF DISSOLVINGLIQUOR BY DISCHARGING A DOWNWARDLY DIRECTED JET OF GASEOUS FLUIDINTERSECTING SAID SMELT STREAM AT A POSITION OF SUBSTANTIAL VERTICALTANGENCY WHILE AT A HIGH JET VELOCITY AND DRIVING SAID DISINTEGRATED ANDDISPERSED SMELT INTO SAID POOL OF DISSOLVING LIQUOR.